To provide a support system which can speedily obtain a construction plan for plant construction and a process plan for periodic inspection construc tion and easily cope with alterations of the process plan even when the process plan is altered.

Plural host computer machines 2 (2-1 to 2-N) are connected to a wide area network 3A and constituted by departmental networks 4 as local area networks. The departmental networks 4 are of network constitution wherein plural terminal devices 3 (3-1 to 3-N) and a server machine 1 for those terminal devices 3 are decentralized and arranged; and the host computer machines 2 support the generation of construction and process plans by machine kinds and fields, and the server machine 1 and terminal devices 3 connected to the departmental network 4 support the generation of plural congested process plans by the machine kinds and fields by administered by the departmental networks 4.